A standard baffle assembly of the type used in a catalytic converter for processing the exhaust gases of a motor-vehicle engine has a housing holding a baffle assembly forming a multiplicity of passages through which the exhaust gases flow. The baffle assembly is formed as a stack of baffles that each form a plurality of parallel passages and the baffles themselves are catalyst supports, that is they are typically formed of or coated with the catalyst in question.
As a rule the process entails the catalytic conversion of carbon monoxide (CO), nitrogen oxides (NO.sub.x), and hydrocarbon residues (C.sub.m H.sub.n) into harmless gases, mainly carbon dioxide (CO.sub.2), oxygen (O.sub.2), and nitrogen (N.sub.2). Typically the catalyst is platinum based and is applied as a surface layer to the metal normally forming the baffles. For such a converter to work well the gases must be intimately contacted with the catalytic surfaces while above a certain temperature. There is however an upper temperature threshold that must be avoided to prevent damage to the catalyst. Thus it is critical to get good flow through the converter in such a manner that all the molecules in the passing gases at some time come into contact with the catalyst, thereby also ensuring good uniform heat transfer and that the baffles are maintained in the desired temperature range.
A standard baffle is formed as a corrugated metal sheet sandwiched between a pair of flat sheets. It is also known to form the entire baffle assembly as an extruded ceramic body formed with a multiplicity of longitudinally throughgoing passages. Thus the baffle assembly forms a honeycomb having a plurality of full-length passages. In order to maximize heat transfer and catalyst/gas contact, each passage is relatively small in cross section, typically about 1 mm.sup.2, and is about 100 mm long. The flow in such passages is wholly laminar, but due to the small cross section relatively good contact with the passage walls is ensured.
Such arrangements present a relatively large resistance to flow due to the small passage size. Furthermore they tend to heat up excessively at the center so that the catalyst can be burnt off while not heating up enough at the outer periphery and intake end to ensure catalytic action there. A burning particle can easily lodge in such a baffle assembly and block and/or damage it.